Keg/Sanitation Question

I read a thread about sanitizing CO2 lines and it seemed that some people did and some didn't. I decided not to and other than the initial sanitizing and didn't sanitize immediatly before hooking the keg up. I have three beers on tap 2 of which taste good and one tastes crappy. It has a funky smell and weird aftertaste. I primed the keg and let it carb naturally for a week so I'm not sure if it is yeasty trub from the bottom of the keg or if its infected. My sanitization procedures are good, i star san'd everything. I guess im paranoid about ruining the other two batches because their hooked up to a common co2 manifold if this one is indeed infected. Part of me thinks that Im being overly paranoid and should relax and wait it out to see if the beer is just green or is getting yeast sediment from the bottom. ANy advice?

I've never sanitized my CO2 lines, but I am very careful not to get beer or any fluids in them. I did once and then I replaced them.